Radially-Coherent Writing
It is common in the art that data be written to a plurality of concentric (about a rotation axis RA of a magnetic disk) circular data tracks on a magnetic disk. The written data is “radially-coherent” in a range of radial positions along the respective data tracks if for each radial position in that range, the bits of the written data start from the same (or a “common”) radially-extending reference line on the magnetic disk, and all magnetic transitions along the respective data tracks are aligned with one of a set of uniformly spaced-apart (by a bit period) radially-extending inter-bit boundary lines.
FIG. 1 and FIG. 2 illustrate radially-coherent writing on a magnetic disk and non-radially-coherent writing on a magnetic disk, respectively.
FIG. 1 shows a small area of an exemplary magnetic disk 111 after radially-coherent writing has been performed along five mutually adjacent data tracks 30. In FIG. 1, the horizontal direction represents a circumferentially-extending direction along the circular data tracks, and the vertical direction represents a direction along a radius of the circular data tracks. The data writing at each track 30 always starts from the same radially-extending reference line 10. The dashed vertical lines 20 in FIG. 1 depict the regularly spaced bit boundary lines to which the magnetic transitions are aligned. The positive polarity of media magnetization is shown in black, while negative polarity is shown in white.
FIG. 2 shows a small area of the magnetic disk after non-radially-coherent writing has been performed along the same five mutually adjacent data tracks 30. In FIG. 2, the writing at various radial positions 30 does not start from a common radially-extending line, like line 10, and the magnetic transitions are not aligned with radially-extending inter-bit boundary lines 20 which are at points regularly spaced from reference line 10.
Radially-Coherent Reading
Data is read from a magnetic disk in “radially-coherent” manner in a range of radial positions, if for each radial position in that range, the read-back signal from a magnetic head starts from the moments in time when the head flies by the same radially-extending reference line on the magnetic disk. The technique of radially-coherent reading can be applied to the reading of either radially-coherent or non-radially-coherent written data.
FIG. 3 illustrates radially-coherent reading for radially-coherent written data. For each of written tracks 31-35, corresponding read-back signals 51-55 from a magnetic head are shown. For better demonstration of alignment, the read-back signals are shown superposed with the media magnetization. The radially-coherent reading for each radial position 31-35 on the respective data tracks always starts from the same radial reference line 10.
The ability to write radially-coherent data, and read it back in radially-coherent manner, is important for testing of magnetic heads and magnetic disks.